1. Technical Field
The present invention relates in general to data storage systems, and in particular to reducing the time required for initializing a data storage array. More particularly, the present invention relates to a method and system for moderating a disk array startup sequence during a multi-disk power-up cycle. Still more particularly, the present invention relates to a method and system for adaptively determining and implementing a disk array startup policy that minimizes the time required to perform a multi-disk startup sequence in accordance with dynamic power supply capacity and spindle motor startup metrics.
2. Description of the Related Art
Disk drives attached to a Small Computer System Interface (SCSI) bus or a Peripheral Component Interconnect (PCI) bus may employ different configurations. “JBOD”, an acronym for Just a Bunch of Drives referring to multiple hard disk drives connected to an adapter on the data processing unit with no special treatment of data among the drives, is one such configuration. A disk array or Redundant Array of Independent Disks (RAID), is a group of hard disk drives controlled by a single adapter/controller and combined to achieve higher transfer rates than a single drive, is another. In the latter configuration, even though multiple disks are controlled by one adapter, the RAID system appears as one drive to the host data processing system. Depending on the configuration, the RAID system will increase the level of protection and storage capacity for a data processing system over a single hard disk drive. The primary functions of the RAID system are to increase the availability, protection, and storage capacity of data from a data processing system.
High-end storage arrays, such as RAID arrays, have been widely implemented in support of large-scale single-user and multi-user data storage systems. The proliferation of networked (i.e. multi-user) data storage devices, such as within storage area networks (SANs), has given rise to the development of shared disk volume partitioning, sometimes referred to as virtual shared partitioning. Virtual shared partitioning facilitates seamless access from multiple, possibly geographically remote, client devices to multiple servers in which the multi-drive arrays reside. High performance partitioned data storage servers within individual Network Area Storage (NAS) facilities are the building blocks of current SANs.
Implementation of virtual shared partitioning within a given NAS facility often requires an adjustment, or realignment, of shared data resources. Some logical volume realignments can be implemented on-the-fly without the need to deactivate (i.e. power down) any of the currently active disk drive arrays. However, if the need for logical volume realignment results from, for example, a failure in a server hosting an object disk drive array, the “bad node” may have to be taken offline resulting in the object disk drive array having to be deactivated. Service operations, such as server updates or redeployment, may also necessitate the host server being taken offline, again resulting in the resident disk drive array being deactivated.
It is imperative for many business-related NAS applications, that the server down time be minimized to the extent possible. One source of delay in bringing a given server back online is the time required to perform the requisite power-on sequence (sometimes referred to as boot time) in which the drive array disks are “spun up”. Disk drive spindle motors consume considerably more current during transient startup periods than during steady state spindle motor operations. The desire to minimize power supply costs, results in provision of power supply resources in conformity with the steady state power supply requirements. However, the aforementioned disparity in power supply requirements results in inadequate power supply resources to accommodate a simultaneous spin-up of all disks within a given drive array. Therefore, there is typically a need to determine an appropriate start up sequence in which power supply resources are not overtaxed at any given time during a disk drive power on interval.
The problem of determining an optimal disk drive startup sequence is addressed in U.S. Pat. No. 5,673,412, U.S. Pat. No. 6,131,142, and U.S. Pat. No. 6,286,108 B1, all issued to Kamo et al. (hereinafter “Kamo”). Specifically, Kamo addresses the need to moderate a disk drive startup procedure by predetermining a number of disk drives groups in a disk system and starting each of the constituent disk drive groups in a sequential manner. Fundamentally, Kamo's approach to disk array spin-up comprises dividing the disk drives into designated staggered startup time slots in accordance with the increasingly diminished power supply resources available as more drive groups are spun up. The object of Kamo's startup policy is to perform a disk drive array spin-up within a prescribed period of time while observing power supply limitations.
While providing a means to avoid overtaxing power supply resources, the disk drive startup sequence as described by Kamo does not address several key factors that affect the ultimate efficiency, in terms of reducing array spin-up time, of the selection of disk drive startup groups. One such factor, is the spin-up time required by each of the individual disk drives which constitute a given startup group. In addition to failing to incorporate individual drive spin-up times as part of the drive group selection function, Kamo's drive array startup policy does not address optimizing the disk drive startup group determination to dynamically (between each distinct disk drive array startup interval) account for interim changes in power supply capacity and individual drive power consumption requirements.
It can therefore be appreciated that a need exists to address the foregoing deficiencies in prior art disk array spin-up procedures. The present invention addresses such a need by implementing an adaptive disk drive array startup procedure that accounts for updated power supply capacity metrics as well as updated disk drive startup metrics each of which significantly contributes to a startup sequence policy that is dynamically suited to minimizing the overall time required to spin-up a disk drive array.